We know that a number of young Americans have gone to fight for ISIS. We know that at least 500 young British men (and a few women), some of them not much more than teenagers, have done the same.

What we don't know is how many young Irish Muslims have gone to fight in the region. That number is likely to be very small, although it is known that a few went from here to fight against Gadaffi in Libya and more recently against Assad in Syria.

It was in the war against Assad, still being fought by disparate groups, that ISIS really got going and morphed into the murder machine that has mushroomed out of Syria and across northern Iraq. Whether any of those who went out from Ireland joined ISIS we don't know.

We do know that a few years ago garda (police) sources here were saying that they were monitoring a number of al-Qaeda operatives who were based here. These included several men who had come here as asylum seekers up to a decade earlier and who are now Irish citizens.

Some of those being watched by the gardaí regularly went missing from their Irish addresses for months at a time. Others were known to be part of an international “charitable” organization which was funneling money to Bin Laden.

The phenomenal level of immigration into Ireland during the boom years, a considerable amount of which came from Middle Eastern and North African countries, now poses a real challenge for security here.

The Irish Independent this week reported that a joint watch list on suspect jihadi fighters is being operated by the Irish and British authorities to prevent terrorists slipping into either jurisdiction through a back-door route. Immigration officers are already sharing information about visa applicants and this is being ramped up dramatically to include cross-checking airline passenger lists and sharing fingerprint data.

The Irish media always emphasizes how peaceful the Muslim community in Ireland is and how its members are a valued part of our new multi-cultural society. In recent weeks, as the shocking ISIS massacres and beheadings have made international headlines, some leading figures from the Irish Muslim community have been interviewed on radio and TV here to reassure people that there is no support for ISIS among Muslims in Ireland.

That may well be true, but it is also true that is it extremely difficult even for them to know whether any young Muslims here have been radicalized.

We have seen what has happened in the US and in Britain, where young Muslims who appeared to be all-American kids and typical British youngsters have turned up on TV as full blown terrorists.

Despite being American born or British born, despite having gone to school and college and being into all the things that other teenagers are into like music, social media and sports, somehow they end up squatting in the sand in Syria or Iraq waving guns and spouting jihadi threats against the west. And even their parents had not realized what was happening to them.

The extent to which this has happened in Britain is very alarming and has left British politicians shocked and perplexed about what to do. According to the security services in the U.K., at least 500 and possibly up to 700 people, mainly young men, have gone from the U.K. to Syria and Iraq. The big question is what they may do when, battle-hardened and even more radicalized, fanatical and embittered, they come back.

Even identifying them is difficult. Tens of thousands of people from Britain and Ireland every year go on holiday to beach resorts in Turkey, which borders Syria. There are other routes also to Iraq via other countries in the region.

Or you can fly for a "holiday" to Greece, which is next door to Turkey. And of course it is possible for people to cover their tracks by flying to another European city before traveling onwards over land.

So how do you prove whether someone is coming back from Syria or Iraq? The threats by British politicians to isolate returning fighters or to confiscate their passports are likely to be difficult if not impossible to implement. And our border with Northern Ireland makes it impossible for us to stop people returning from the region through the U.K.

One consequence of all this is that it has put a very large question mark over the politically correct mantra that is fed to us all the time from government sources and government sponsored organizations that work with immigrants that a multi-cultural society is by definition a good thing.

In a huge melting pot country like the U.S. that is easy to argue, although even there it is not without difficulties. In smaller European countries with no long term history of immigration, however, it is a different matter.

The multi-cultural message here and elsewhere in Europe has always been a somewhat contradictory one.

On the one hand it urges acceptance and support to allow the different cultures and beliefs of immigrants to be maintained. On the other hand it urges a high level of funding to help the new arrivals to fully integrate.

Large scale immigration here in Ireland is a very new phenomenon, going back just 20 years. In the U.K. it goes back to the 1950s, with most immigrants coming from former British colonies and therefore having some identification with Britain.

Even in Britain, however, what has now been exposed by the numbers going to fight for ISIS is the degree to which multi-culturalism has failed.

On a less dramatic level, that failure has been evident for many years in towns across the north of England and in other poorer areas where whole neighborhoods are now home to Indian or Pakistani immigrants.

Instead of integrating, many of these people have congregated together in their own areas and streets – much like the Irish do when they emigrate – and even after decades in Britain some of the older ones still speak little English. Their children go to local schools and are as British as anyone else, but sometimes there are tensions that, for a minority, can turn into resentment and disconnection with the wider society.

There have been some startling examples of this and of the fact that cultural differences don't simply vanish overnight, or even after a generation.

The most stark example was the report published just over a week ago into sexual abuse in Rotherham, a town in Yorkshire in the the north of England. (If you Google Rotherham you will find it.) This detailed how 1,400 young white girls had been abused over a 20 year period mainly by Pakistani men in the area.

The scale of it was extraordinary and the details were horrifying, with most of the young girls being from poor, dysfunctional families or care homes and some of the Pakistani men being cab drivers who picked them up and groomed them with sweets and alcohol before passing them around. The story has become a big scandal because the police were informed on several occasions about what was going on but did not act because it might upset racial harmony in the area.

One interesting aspect to the case was the attitude of the local Pakistani men to the girls, who they regarded as worthless young sluts with no morals, unlike their own Muslim women who dressed modestly and behaved correctly.

Another worrying example of the failure of multi-cultural Britain was the revelation recently, again in some towns in the north of England, that strict Islamic rules were being imposed in some schools in areas where Muslims had a majority on local school boards, despite the fact that the curriculum for schools is agreed at national level. Again, failure by teachers and others to confront this was due to a fear of being accused of racism.

The fact is that despite all the effort put into creating a multi-cultural Britain, it has been only a limited success. Separate lives are lived by different communities in some areas and there is little sense of a common society.

However, this does not fully explain the disconnect some young Muslims in Britain feel and the way their resentment can grow to the point where they hate the society they live in and they become so disillusioned that hundreds of them have joined ISIS and other radical groups. But it does show that blinkered political correctness can be dangerous and that we ignore the problems of a multi-cultural society at our peril.

A big part of the ISIS problem is what Marx called the opium of the masses, religion, which is something we know a good deal about in Ireland.

The differences between Islam's two big sects, Shia and Sunni, may seem so slight to non-Muslims that it seems incredible they are slaughtering each other because of them. (It has to do with which relatives are the legitimate successors to the prophet Muhammad who died in 632.)

But then is there really all that much difference between being a Catholic and a Prod?

The new found fanaticism of some of the young ISIS recruits from the U.S. and the U.K. may be almost comical. But that does not make it any less deadly. Just as in our own history, religious differences can lead to great inhumanity.

Of course the ISIS threat is about political control as well as religion. The straight lines drawn across places in the Middle East by the colonial powers are a major part of the ongoing problems in the region.

Like it was here, land is part of the problem. Here, however, land and political control were always the primary factor in our troubled history rather than just religious difference.

That is not the case with fundamentalist Muslims and particularly with groups like ISIS, whose religious certainty demands they impose their extreme beliefs on everyone else and is used to justify extraordinary savagery.

In Ireland, following the mass immigration during the boom, there are now streets in some of the poorer suburbs of Dublin and in the inner city where there is a concentration of groups of immigrants. There are ongoing problems in these areas, although they rarely get much attention, again because of political correctness.

Might there be some young Muslims here who feel rejected by Irish society, who are seething inside with resentment and who are looking for a cause to give meaning to their lives?

The answer is we just don't know. But we need to be vigilant.

“It was either fight with ISIS or they will kill me” admits former Islamic State fighter.Wikimedia